How to assign specific values to pixels?

I have a large matrix with pixel values ranging from 0 to 255 and I would like to assign specific values (map) from a txt file (table).

I have looked at other similar questions on this forum but they were focused on replacing a couple of values with "if" conditions which doesn't apply to my case since i have a large matrix.

Here is an example:

Thanks

m = [1 22 33;44 55 66;77 188 255] % pixel default value

m = 3×3

1 22 33 44 55 66 77 188 255

values = [1 1;22 4;33 9;44 35;55 48;66 90;77 99;188 200;255 300] % txt file 

values = 9×2

1 1 22 4 33 9 44 35 55 48 66 90 77 99 188 200 255 300

M = [1 4 9; 35 48 90; 99 200 300] % expected result

M = 3×3

1 4 9 35 48 90 99 200 300

Answer 1

[Stephen23]

m = [1,22,33;44,55,66;77,188,255] % pixel default value

m = 3×3

1 22 33 44 55 66 77 188 255

v = [1,1;22,4;33,9;44,35;55,48;66,90;77,99;188,200;255,300] % txt file

v = 9×2

1 1 22 4 33 9 44 35 55 48 66 90 77 99 188 200 255 300

[X,Y] = ismember(m,v(:,1));
m(X) = v(Y(X),2)

m = 3×3

1 4 9 35 48 90 99 200 300

Compare against your expected output:

M = [1 4 9; 35 48 90; 99 200 300] % expected result

M = 3×3

1 4 9 35 48 90 99 200 300

[Moïra Benmenni]

Thank you very much that is exactely what i needed!

Answer 2

[Image Analyst]

Use the function made for this kind of operation : intlut().

Not sure how many thousands or millions of rows your large matrix is but it should work. If your matrix is too huge, like many gigabytes and billions of pixels, then you're going to have problems anyway, regardless of this function.